While I’m still waiting on parts and hemp fibre to arrive I decided to have another go at making a composite joint with fibreglass resin, sisal twine and a 3-way bamboo mitred bamboo joint.
Here’s the workspace:
Here’s the initial binding of the sisal, with a coat of Timber Sealer applied (this stuff helps the epoxy resin stick to the wood):
Here’s the 2nd layer of sisal applied and it all drenched in epoxy:
It may not look too crash hot at the moment, but remember this is just the first layer. Once this is dry I’m going to use a more putty like builders epoxy to allow me to mould the shape of the join better.
here’s the first layer sanded back, ready for the filler epoxy layer:
I’ve recently decided to build a cyclocross frame for the first prototype. I figure if anything’s going to test out the durability of a frame it’ll be a cyclocross race. That and it’s the only sort of bike I don’t own that I’ve always wanted (apart from a recumbent, unicycle, downhill, fixie, penny farthing …).
Here’s how it’s looking so far (ignore the colours, I just like designing in red/black/white):
As you can see there’s lots of angles, lengths and diameters to figure out. The BikeCAD above only is only showing the basic frame dimensions and angles, not any of the mitre lengths or tubing diameters.
The main issue to solve with using bamboo is tyre clearance for the chain and seat stays. I’m picturing that the diameter of this bamboo will be slightly larger than a steel/alu/carbon bike in order to get the greatest stiffness. To help overcome the larger than normal tube diameters I’m using a 73mm bottom bracket as well as a wider than normal seat stay attachment angle. If that doesn’t alleviate the problem I’ll try using skinnier bamboo, but fill it with expanding foam filler, which I’ve been told increases stiffness markedly.
The drop outs, bottom bracket, seat tube sleeve and head tube have all been ordered and are on their way. Soon it’ll be mitre time!
I’ve selected the 7 culms (fancy word for a bamboo pole) for the first frame. Here’s a pic of them laid out into the respective parts of the frame:
And here’s a view of the thickness of the downtube:
I also ventured to my local hardware store and picked up some epoxy resin, glass coat, borax, beeswax and some other glues and finishes to test the curing and joint making processes with:
I haven’t managed to find Boric Acid anywhere yet thou. I suspect I’ll be able order it online somewhere, or it might be available at a chemist.
I’m starting a journey of discovery into 2 things. The way of bamboo and the way of the bike frame. I plan on making 2 prototype bikes with mostly bamboo frames. One with lugged steel joints, the other with woven fibre and epoxy resin. Based on the successes or failures of each prototype I then plan on producing custom frames for demanding customers who’re after something a bit different in their daily ride.
The prototype bikes are going to be simple single-speed flat-bar commuters, similar in geometry and style to a Giant CRX or Apollo Blade.
Using BikeCAD and a tape measure I’ll measure and design the requirements for each frame, and decide upon what’s going to be bamboo, and what’s best left to steel or other material.
I’ve sourced enough bamboo (from my kind parent’s garden) for two bikes. But before I can use it I need to cure and treat it against bugs, mould and cracking. Hopefully I’ve got enough to play with after all the experimenting!
After treating the bamboo I’ll be examining diameters to see which will best suit the various parts of the frames. From there I’ll explore the joining process with metals and other materials.
Protecting the bamboo against the elements will also require some research. What oils, paints or varnishes can I use?
This site will seek to be a resource of information about bamboo bikes as well as a documentation of the building process from start to finish for others to follow.